1. Field of the Invention
The present invention relates to a ventilator for respiratory treatment, of the type having gas delivery means, regulating means arranged to control the gas delivery means to deliver gas to a patient to obtain sufficient ventilation and sensing means for detecting an apnea of the patient, the sensing means being connected to the regulating means which are disposed to control said gas delivery means to deliver gas to the patient according to prescribed parameter values, if an apnea exceeding a predetermined length is detected.
2. Description of the Related Art
A common problem encountered in the practice of critical care medicine is that a severely ill patient will "fight" the ventilator, that is respiration efforts by the patient are non-synchronous to the operation of the ventilator. This problem can give rise to pain, hypoxia or hypoventilation of the patient. It is of utmost importance in such a situation that the ventilation pattern delivered by the ventilator and set by a clinician does not restrict the patient's own desired breathing pattern, as this might inflict damage to the lung.
If this situation occurs and the ventilator is operating in a so-called controlled ventilation mode, that is in a mode in which the ventilator is working according to preset parameter values, each respiration effort by the patient will be rewarded by the delivery of one tidal volume as set by the clinician, no more and no less, and this only under the presumption that the triggering level of the ventilator has been set judiciously so the patient can trigger a ventilator delivered tidal breath. To cope with this situation, common practice is to sedate the patient and administer a neuromuscular blocking drug, which will induce muscle paralysis and stop further respiration attempts by the patient. The use of neuromuscular blocking drugs in intensive care has, however, been frequently criticized, because of lack of knowledge about the effects of longterm usage.
Another way of handling the problems in connection with non-synchronism between the operation of the ventilator and the respiration efforts of the patient is to manually change the breathing mode of the ventilator, so the respiration of the patient is supported by the ventilator, thereby allowing the patient to breath spontaneously and receive proper pressure or volume support. This operating mode of the ventilator will give the patient the possibility to breath at his own leisure and give the clinician time to analyze the state and then take proper measures to treat underlying problem in a way other than by using neuromuscular blocking drugs as mentioned above.
The situation of a patient fighting a ventilator, however, can be quite alarming and very often no time is available for analysis, so there is a tendency to treat the patient according to a routine prescription and leave the analysis until the chronic situation is abated. This can prolong the time the patient stays connected to the ventilator, increase the complication rate and deteriorate the clinical outcome.
The above-mentioned modes of operation of a ventilator for respiratory treatment are described in the publication Servo Ventilator 300, Operating Manual, chapter 5, issued by Siemens-Elema AB, May 1993.
Even if the patient is not fighting the ventilator as described above, there is a risk that the patient will spend too long a time connected to the ventilator by using machine controlled ventilation for extended periods of time. This can result in weakening and even wasting of the respiratory muscles of the patient and prolonged time for weaning the patient off the ventilator. Therefore, this situation also presents a risk of increased complication rate and impaired clinical outcome.
The disadvantages of the current ventilator technique thus reside in the fact that the breathing mode determined by the ventilator forms an obstacle to attempts of spontaneous respiration by the patient, and this situation can only be altered by manually changing the settings controlling the operation of the ventilator.